Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Blood dilution during bypass surgery associated with kidney damage

03.09.2003


When physicians routinely "thin" the blood of patients undergoing coronary artery bypass surgery in order to place them on the heart-lung machine, they may be causing more damage to the kidneys and other organs than previously appreciated, according to a new study by Duke University Medical Center researchers.



For years moderate dilution of the blood has been thought to protect the kidneys from damage, but the Duke researchers found in their study of more than 1,400 bypass patients that dilution to the lower levels of accepted ranges is associated with measurable kidney damage. The Duke team published the results of its study in the September 2003 issue of the Annals of Thoracic Surgery.

In order to safely operate on a non-beating heart, physicians attach the body to a heart-lung machine, which takes over for the stopped heart in circulating oxygen-rich blood throughout the body. To prime the pump, physicians add fluid -- usually a balanced saline solution -- to the circuit to fill the tubing and pumping chambers of the machine.


This additional fluid lowers the percentage of oxygen-carrying red blood cells in the blood, a measurement known as hematocrit. Normal hematocrit ranges from 36 to 40 percent. During bypass surgeries, the hematocrit can range from 22 to 26 percent, with even lower percentages being commonly attained at different points during the operation.

"Using hematocrit as a tool to assess a patient’s anemia, we found that the lowest hematocrit achieved during the bypass procedure was significantly associated with acute kidney damage," said Duke anesthesiologist and study leader Mark Stafford-Smith, M.D. "Furthermore, we found the risk to kidneys increases as a patient’s body weight increases.

"This is the first report highlighting the association of hemodilution during bypass surgery with acute injury to the kidneys," Stafford-Smith continued. "Our findings question the wisdom of tolerating the lowest levels of hematocrit during bypass surgery."

Transfusing additional blood is not considered an ideal solution, Stafford-Smith said, since this and other studies have shown that transfusions are also associated with kidney damage. He recommended that more attention be paid to shortening the bypass circuit or using smaller diameter tubing to reduce the levels of hemodilution.

Every year, more than 750,000 patients worldwide undergo bypass surgery, and researchers estimate that about one of every 12 will suffer kidney damage as a result of the surgery. While most cases of kidney injury are transient, up to 2 percent of bypass patients will require kidney dialysis, with 60 percent of those dying before hospital discharge, Stafford-Smith said.

One commonly accepted benefit of hemodilution has been that it makes the blood less viscous, Stafford-Smith said. Also, it has been thought that since body temperature is lowered during surgery, there were enough red blood cells in the diluted blood to satisfy the tissue’s reduced need for oxygen. Stafford-Smith said that the physicians want to minimize the use of donated human blood to prime the heart-lung machine pump.

Other studies have suggested that the lowest hematocrit levels reached during surgeries may be linked with worse outcomes, so Stafford-Smith and his colleagues consulted the medical records of 1,404 patients receiving bypass surgery at Duke University Hospital to answer the question.

He correlated hematocrit levels during surgery with levels of creatinine -- a byproduct of normal metabolism -- in the blood before and after surgery. Kidneys normally filter creatinine out of the blood and excrete it in the urine, so higher-than-normal levels in the blood indicate that the kidneys’ ability to filter blood has been impaired.

Interestingly, the researchers found a strong link between the weight of patients and increases in the levels of creatinine in the blood.

"For example, for a patient weighing 165 pounds, there is no association between lowest hematocrit and increased creatinine," Stafford-Smith said. "However, in the 330-pound patient, there is a highly significant inverse association. The significance of the association rises as weight increases.

"For this reason, it is important for physicians to pay special attention to their patients who are overweight or who have existing kidney damage," he said.

Stafford-Smith pointed out that up to 20 percent of patients who are scheduled for bypass surgery have some degree of existing kidney damage, further emphasizing the need for physicians to consider these factors in the care of their patients.

The researchers also looked at the role of transfused blood during bypass. They came to the conclusion that if it seems likely during the course of the procedure that the patient will require a later transfusion, it is best to give that blood before the hematocrit drops to the lowest levels.

"The level of a patient’s hematocrit is a factor that we as physicians have control over, and it is also a factor that is amenable to proper management," Stafford-Smith.

In the course of their studies, the researchers also followed minute-by-minute changes in blood pressure during the period of support on the heart-lung machine and were surprised to find that changes in blood pressure had little effect on kidney damage.

Stafford-Smith’s analysis of the data was supported by the cardiothoracic division of the Duke’s department of anesthesiology.

Members of Stafford-Smith’s Duke team were Madhav Swaminatham, M.D., Barbara Phillips-Bute, Ph.D., Peter Conlon, M.D., Peter Smith, M.D., and Mark Newman, M.D.

Richard Merritt | EurekAlert!
Further information:
http://www.dukemednews.org/

More articles from Health and Medicine:

nachricht Nanoparticles as a Solution against Antibiotic Resistance?
15.12.2017 | Friedrich-Schiller-Universität Jena

nachricht Plasmonic biosensors enable development of new easy-to-use health tests
14.12.2017 | Aalto University

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First-of-its-kind chemical oscillator offers new level of molecular control

DNA molecules that follow specific instructions could offer more precise molecular control of synthetic chemical systems, a discovery that opens the door for engineers to create molecular machines with new and complex behaviors.

Researchers have created chemical amplifiers and a chemical oscillator using a systematic method that has the potential to embed sophisticated circuit...

Im Focus: Long-lived storage of a photonic qubit for worldwide teleportation

MPQ scientists achieve long storage times for photonic quantum bits which break the lower bound for direct teleportation in a global quantum network.

Concerning the development of quantum memories for the realization of global quantum networks, scientists of the Quantum Dynamics Division led by Professor...

Im Focus: Electromagnetic water cloak eliminates drag and wake

Detailed calculations show water cloaks are feasible with today's technology

Researchers have developed a water cloaking concept based on electromagnetic forces that could eliminate an object's wake, greatly reducing its drag while...

Im Focus: Scientists channel graphene to understand filtration and ion transport into cells

Tiny pores at a cell's entryway act as miniature bouncers, letting in some electrically charged atoms--ions--but blocking others. Operating as exquisitely sensitive filters, these "ion channels" play a critical role in biological functions such as muscle contraction and the firing of brain cells.

To rapidly transport the right ions through the cell membrane, the tiny channels rely on a complex interplay between the ions and surrounding molecules,...

Im Focus: Towards data storage at the single molecule level

The miniaturization of the current technology of storage media is hindered by fundamental limits of quantum mechanics. A new approach consists in using so-called spin-crossover molecules as the smallest possible storage unit. Similar to normal hard drives, these special molecules can save information via their magnetic state. A research team from Kiel University has now managed to successfully place a new class of spin-crossover molecules onto a surface and to improve the molecule’s storage capacity. The storage density of conventional hard drives could therefore theoretically be increased by more than one hundred fold. The study has been published in the scientific journal Nano Letters.

Over the past few years, the building blocks of storage media have gotten ever smaller. But further miniaturization of the current technology is hindered by...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

AKL’18: The opportunities and challenges of digitalization in the laser industry

07.12.2017 | Event News

 
Latest News

Engineers program tiny robots to move, think like insects

15.12.2017 | Power and Electrical Engineering

One in 5 materials chemistry papers may be wrong, study suggests

15.12.2017 | Materials Sciences

New antbird species discovered in Peru by LSU ornithologists

15.12.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>